Spatio-temporal Evolution Characteristics Of Meteorological Drought And Cause In Huai River Basin

Spatial and temporal variations of drought research of huai river basin agricultural drought monitoring has important theoretical value and practical significance in the prevention and control.It is the important commodity grain base in our country,nearly20% of the nation's grain production from the huai river basin.Therefore,the analysis of the spatiotemporal changes and causes of drought is helpful to improve the ability of drought control and drought relief,guarantee food security in our country,promote the sustainable development of economy and ecology.In this paper,the analysis is based on the daily temperature,precipitation and historical drought data of 149 meteorological stations in the Huai River Basin from 1961 to 2016,as well as 16 climate indicators and NCEP/NCAR reanalysis data from the National Oceanic and Atmospheric Administration,Firstly,a standardized precipitation evapotranspiration index was selected,which comprehensively considered the precipitation and temperature factors.The inter-annual variability,spatial distribution and trend characteristics of the Huai River Basin were systematically analyzed by non-parametric Mann-Kendall tests and empirical orthogonal functions.Secondly,the Copula function of drought duration and drought intensity was fitted,and the appropriate probability distribution function was selected.The causes and effects of the variation of meteorological drought characteristic frequency are studied.Finally,the spatial distribution of the center of gravity of the drought in the Huai River Basin was analyzed by means of wavelet analysis and rotational empirical orthogonal functions to explore the evolution path of the drought in the Huai River Basin,and the main causes of meteorological drought are revealed through the anomalous characteristics of atmospheric circulation.The analysis results are as follows:The results showed that:(1)The correlation between the number of droughts and drought-affected area at the 0.1 significance level,indicating that the SPEI has an excellent suitability in the Huai river basin.The drought time was significantly different and drought frequency was obvious fluctuation in the Huai river basin.The most ofsevere drought and extreme drought is the largest in 1960s(24.8%),followed by 2010s(15.8%)and lowest in 1980s(10.0%).The spatial distribution of drought has much difference.The drought severity was change between 27.76% and 36.04% in the Huai river basin.The drought severity in the northwest and southeast is lower than that in the southwest,northeast and central regions.(2)The spatial distribution of the drought center mainly decreased from the center of Huai River Basin to the surrounding area,and large-scale region of the Huai River Basin showed a trend of drought.The drought center changed from the northwest?the central?the southwest? the central in typical years and the drought center moved to the basin center with the increase of region scale.The results showed that trend of regional drought had a tendency towards drought conditions,which was the decreasing from the central to the surroundings in the Huai river basin.There were three anomaly distribution modes in Huai River Basin: with the same anomaly in whole area,with opposite anomalies in the south and north or in the east and west.The principal modes of our results indicated obvious variation and consistent.(3)The 16-frequency distribution function is used to study the drought duration and intensity of 149 stations in the Huaihe River Basin.The results of NLog L,BIC,AIC,and AICc tests show that the exponential distribution function had the best fitting degree.Twenty-six kinds of multivariate distribution functions were selected to systematically analyze the drought duration and drought intensity of five meteorological stations in the Huaihe River Basin.AIC,BIC,Max-Likelihood,RMSE,and NSE were used to test the Clayton Copula function for optimal fitting.(4)Univariate study The duration and intensity of drought under different recurring periods correspond to the duration and intensity of drought in the northeast> southwest>middle> southeast> northwest.In the two-dimensional joint distribution of drought characteristic variables,from the probability of occurrence of drought,the severity of drought events in the Huaihe River Basin is Fuyang Station> Xixian Station> Bengbu Station> Hongze Station> Linyi station.When drought events occur,the tributary is more severe than the mainstream,the downstream is more severe than the upstream,and the upstream is more severe than the middle stream.(5)PDO,ONI,Nino4,Nino3.4,MEI,BEST were positively correlated with SPEI(p<0.05),while SOI,TNI were negatively correlated with SPEI(p<0.05).The drought cycle is mainly concentrated in 1970 s,1990s and 2000 s,with 2-5a significant cycle(p<0.05),while there was 3.4-4.5a significant cycle(p<0.05)of the climate index.In spring,the airflow in the high latitude area moved southward,and the airflow in the Indian Ocean and the bay of Bengal moved northward,leading to the moisture in the south and the dryness in the north.The weak Mongolian cyclone and the abnormal northerly wind cover lead to the east dry and west wet in summer.The continental high pressure dominates in autumn,and the north wind and south wind influence each other to cause the east dry and west wet.The climate characteristics of east wet and west dry caused by the prevailing downdraft and the prevailing southeast wind in winter.